A direct-illumination type liquid crystal display apparatus, in general, includes a liquid crystal display panel that displays an image and a plurality of lamps that supplies a light to the liquid crystal display panel.
In the direct-illumination type liquid crystal display apparatus, a plurality of lamps is disposed under a liquid crystal display panel substantially in parallel with each other to provide the liquid crystal display panel with a light directly. In an edge-illumination type liquid crystal display apparatus, a lamp is disposed at an edge of a light guide plate that is disposed under the liquid crystal display panel, so that the lamp provides the liquid crystal display panel with a light via the light guide plate. That is, in the edge-illumination type liquid crystal display apparatus, the lamp provides the liquid crystal display panel with a light indirectly. Thus, the direct-illumination type liquid crystal display apparatus has a wider light emission surface and higher brightness than those of the edge-illumination type liquid crystal display apparatus.
Since the direct-illumination type liquid crystal display apparatus includes a plurality of lamps, the direct-illumination type liquid crystal display apparatus uses an external electrode in a lamp, which is economical and easy to operate in parallel.
The external electrode has an insertion hole through which one end portion of a lamp tube of the lamp is inserted, and first and second external electrodes are formed at first and second ends of the lamp tube, respectively. An electric power from an external power supply is provided to the external electrode, and then the lamp tube generates a light in response to the electric power provided to the external electrode.
When the lamp tube generates the light, electric current flows from the first external electrode to the second external electrode along the lamp tube that comprises glass, or vice versa in accordance with voltages applied. When the current density is greater than a proper current density, heat is generated in the lamp tube to melt the glass of the lamp tube, thereby causing a pin hole in the lamp tube.
When the pin hole is generated in the lamp tube adjacent to the insertion hole, a heavy metal such as mercury in the lamp tube flows out. Thus, the lifetime of the lamp having the lamp tube decreases. Moreover, the mercury outflow causes environmental problems.